Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting a power headroom report in a wireless communication system.
Related Art
Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). A long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
To increase the capacity for the users' demand of services, increasing the bandwidth may be essential, a carrier aggregation (CA) technology or resource aggregation over intra-node carriers or inter-node carriers aiming at obtaining an effect, as if a logically wider band is used, by grouping a plurality of physically non-continuous bands in a frequency domain has been developed to effectively use fragmented small bands. Individual unit carriers grouped by carrier aggregation is known as a component carrier (CC). For inter-node resource aggregation, for each node, carrier group (CG) can be established here one CG can have multiple CCs. Each CC is defined by a single bandwidth and a center frequency.
In LTE Rel-12, a new study on small cell enhancement has started, where dual connectivity is supported. Dual connectivity is an operation where a given UE consumes radio resources provided by at least two different network points (master eNB (MeNB) and secondary eNB (SeNB)) connected with non-ideal backhaul while in RRC_CONNECTED. Furthermore, each eNB involved in dual connectivity for a UE may assume different roles. Those roles do not necessarily depend on the eNB's power class and can vary among UEs.
The power headroom reporting (PHR) procedure is used to provide the serving eNB with information about the difference between the nominal UE maximum transmit power and the estimated power for uplink shared channel (UL-SCH) transmission per activated serving cell and also with information about the difference between the nominal UE maximum power and the estimated power for UL-SCH and PUCCH transmission on primary cell (PCell). Efficient power headroom reporting method for CA or dual connectivity may be required.